The present invention relates to ground-penetrating radar (GPR) systems and methods, and more particularly to ground-penetrating radar systems and methods for identifying buried objects.
GPR is similar to upward-looking radar used for air traffic control and meteorology, except that the antenna array is directed toward the ground; thus presenting an entirely different set of technical challenges. For example, GPR is used for geophysical applications such as mapping subsurface strata, locating toxic waste sites for remediation, and detecting of unexploded subsurface ordinance.
A GPR system comprises at least one transmitter that transmits an electromagnetic impulse, continuous wave, or swept frequency signal, for example, in the frequency range of 1 MHz to 10 GHz. The system also comprises at least one receiver that receives a reflected waveform. The impulse is short with respect to the wavelength being transmitted. In practice, the impulse can be, for example, one or two cycles. Therefore, GPR systems are sometimes referred to as “impulse” radars.
Subsurface industries such as construction, utility location, environmental remediation, and unexploded-ordnance detection have long sought safe, reliable, cost-effective methods for “seeing into the ground.” The utility location market suffers greatly from inadequate location technologies that result in hundreds of millions of dollars in damages, delays, and lost revenue for utility companies and contractors every year, losses that can be reduced significantly by use of GPR. Three utility locating market segments, can be distinguished by their accuracy and price: (1) One Call; (2) private locating; and (3) subsurface utility engineering (SUE).
“One Call” is a nationwide clearinghouse that provides an alert to all public and private utilities of when and where construction may impact their lines. By law, contractors must register their site with One Call, which in turn contacts all the relevant utilities so they can mark their utility lines. One Call locating systems are based on electromagnetic induction technology. Utility companies, responding to a One Call work order, guarantee accuracy on conductive lines within twenty-four inches horizontally on either side, with no guarantee of depth. With One Call, utility line locations are simply painted temporarily on the ground, easily subject to erosion or destruction. This poor accuracy results in broken utility lines and revenue loss.
Construction, utility, and industrial companies often rely on “private locating.” Private locating provides a greater degree of accuracy than is delivered by One Call. These companies often hire a utility locating company or a geophysics company to apply more expensive and time-consuming locating techniques. Private locating companies typically use electromagnetic induction technology, GPR, and magnetometry. Often this includes excavation, the most reliable and expensive conventional method for determining the exact location of utilities.
Industrial and utility companies, however, frequently require more accurate maps of the subsurface than One Call or private locating can provide. For instance, extra accuracy may be needed while excavating near an oil pipeline because of the rise of breaking a pipe. Or, it may be too costly to accidently cut an interstate fiber optic cable carrying important communications. In such situations, excavators perform a total cost/value analysis, including consideration of risk/cost avoidance. Often, they are more willing to pay higher fees to ensure greater accuracy.
“SUE” can provide more accuracy than One Call or private locating. SUE is a rapidly growing specialty service offered by geophysical and engineering companies. It entails planning and designing utility arrangements before highway or other large infrastructure construction. SUE engineers painstakingly map all discernible utilities at a given site using a variety of conventional geophysical methods. SUE uses electromagnetic induction technology, GPR, and magnetometry. It is generally more costly than private locating services because it uses computer aided design to produce a permanent record of the location of utilities. Even this premium service often only identifies 80% of utilities with certainty, frequently less when unknown non-conductive utilities are present. Further, SUE is very expensive. Accordingly, there is, therefore, a need for systems that overcome the limitations of the conventional techniques.